There are tons of dog breeding programs that have no downside, it's just the ones that do have a downside that are notable. With respect to wild parrots, it's

There are tons of dog breeding programs that have no downside, it's just the ones that do have a downside that are notable. With respect to wild parrots, it's not obvious that improvement is possible, let alone has disadvantage. Assuming it is possible, there are numerous reasons why it might not already exist. No advantage, low negative advantage, negative incremental advantage, and low probability are all possible reasons. Not every viable state has a viable incremental path to it.